The denialosphere is a desperate sort of place. In it, you’ll hear whoppers like “humans aren’t responsible for the increase in carbon” or even sillier, “CO2 isn’t a pollutant, it’s life!” Every once in a while, however, there arises an argument that isn’t quite so absurd on its face which may require a bit of doing to debunk.
For years, Henrik Svensmark has championed the idea that the current warming can largely be attributed to the variance of cosmic rays and subsequent reduction of cloud nuclei- a hypothesis that has been slightly inconvenienced by the lack of supporting evidence. You can read a succinct and rather amusing take down in Gavin Schmidt’s review of Svensmark’s book for Physics World.
Back in April, a study published in ERL by Sloan and Wolfendale put the matter to rest for the few rational proponents of the theory that remained. However most lunatic denialists like Senator Jim “[global warming is the] greatest hoax ever perpetrated on the American people” Inhofe aren’t rational people, and the good Senator has propped this little mole back up once more (“cosmic rays” appears at least 25 times in his latest round of FUD).
Unfortunately for Inhofe, his timing couldn’t be worse, as a further debunking of the idea has recently been published in Atmospheric Chemistry and Physics. The study, led by Jon Egill Kristjánsson, went further than Sloan and Wolfendale’s paper from earlier this year and examined MODIS data since 2000 allowing the team to examine cloud factors in addition to cover such as droplet size, depth, and water content. The study concludes:
The overall conclusion, built on a series of independent statistical tests, is that no clear cosmic ray signal associated with Forbush decrease events is found in highly susceptible marine low clouds over the southern hemisphere oceans. Whether such a signal exists at all can not be ruled out on the basis of the present study, due to the small number of cases and because the strongest Forbush decrease events indicate slightly higher correlations than the average events… For the ongoing global warming, however, the role of galactic cosmic rays would be expected to be negligible, considering the fact that the cosmic ray flux has not changed over the last few decades…
Of course, a lack of observable evidence has yet to prove a limiting factor for denialists’ claims. For the rest of us, though, this is yet another nail in the coffin of the cosmic ray argument.
[LATE, LATE UPDATE: New study again refutes the alleged causation.]